1. Field
The presently disclosed subject matter relates to a vehicle light used as a headlight, an auxiliary headlight, a signal light, vehicle or traffic light, and the like.
2. Description of the Related Art
FIG. 1A and FIG. 1B show a conventional projector type vehicle headlight.
The vehicle headlight 1 shown here is configured as a single light fixture. The vehicle headlight 1 is configured to include a bulb 2 serving as a light source, an elliptical reflecting surface 3, a projection lens 4, and a light shielding shutter 5. The elliptical reflecting surface 3 has a first focus F1. The light emission center of the bulb 2 is positioned close to the first focus F1. In addition to this, the elliptical reflecting surface 3 is arranged such that the major axis thereof coincides with the optical axis of the bulb 2 and reflects light from the bulb 2 towards the front. The projection lens 4 is arranged such that the position of the focus thereof on the light source side is positioned close to the position of a second focus F2 of the reflecting surface 3. This configuration allows the projection lens 4 to focus light from the bulb 2 or the reflecting surface 3. The light shielding shutter 5 is arranged within the light path from the bulb 2 to the projection lens 4 as well as close to the second focus F2 of the reflecting surface 3 to shield part of the irradiated light and form a cutoff portion in the light distribution.
In this instance, the vehicle headlight 1 utilizes a bulb referred to as a C-8 light source for the bulb 2. The bulb 2 is arranged facing forward such that the center axis thereof extends towards the front almost horizontally coinciding with the optical axis of the projection lens 4.
The intensity distribution of the C-8 light source is comparatively low in the front and back end portions (longitudinal direction) and is also comparatively high in the upper/lower and left/right directions (the radial direction, e.g., the directions perpendicular to the longitudinal direction).
Therefore, the bulb 2 is installed from the rear of the reflecting surface 3 and the light that is emitted in this perpendicular direction (radial direction) is reflected on the reflecting surface 3 towards the front. Because of this, the light intensity of the irradiated light is strengthened.
The projection lens 4 is, for example, formed from a convex lens with an aspheric surface and is secured and maintained in position with respect to the reflecting surface 3 through a lens holder 6. The light shielding shutter 5 is installed between the reflecting surface 3 and the lens holder 6.
The light emitted from the bulb 2 in the vehicle headlight 1 with this type of configuration either is directly incident on the projection lens 4 or is reflected on the reflecting surface 3 and then incident on the projection lens 4 after being focused towards the second focus F2 of this reflecting surface 3. The incident light is focused by the projection lens 4 and is then irradiated towards the front.
At this time, part of the light incident on the projection lens 4 is blocked by the light shielding shutter 5. Thus, a cutoff portion is formed in the light distribution pattern without glaring light being presented to opposing vehicles. In other words, desired light distribution properties (refer to FIG. 2) are obtained which shorten the irradiation distance on the opposing driving lane. A so-called passing-by beam (hereinafter referred to as a low beam) is thus formed.
When forming a travel beam (hereinafter referred to as a high beam), the light shielding shutter 5 is removed from the light path so that a cutoff portion is not formed.
The C-8 light source bulb in the vehicle headlight 1 with this type of configuration is arranged facing forward with the lengthwise direction of the bulb coinciding with the optical axis. Because of this, the length of the entire light fixture in both the forward and rearward directions becomes comparatively longer requiring a large installation space with respect to the body of the vehicle. In addition, the degree of freedom in which the installation can be performed is reduced placing restrictions on the body design of the vehicle.
In particular, when using a high intensity discharge (HID) light source as the bulb 2, a comparatively large power feed socket incorporating one portion of the igniting device is required in order to drive and illuminate the HID light source. For this case, the length of the HID light source itself in the longitudinal direction is approximately 100 mm. Consequently, the length of the entire vehicle headlight 1 is approximately 180 mm.
The overhang (portion stretching from the axle to the end of the vehicle) of the front of a vehicle in modern automobiles is short. In addition, vehicle body shapes which take into consideration aerodynamic performance and round off the four corners of the vehicle body to greatly reduce the surface area are often used. There are also trends to combine wide tires that have a large oblateness and large diameter wheels. These cause severe restrictions on the installation space required to install a vehicle headlight. This has resulted in greater demands to shorten vehicle headlights in at least the longitudinal direction.
On the other hand, from the viewpoint of improvements to safety and differentiation of performance, the installation ratio of HID light sources which are longitudinally long is often desired in order to increase the light intensity. In recent years, the use of headlights with variable light distribution for curved paths have come to be recognized as adaptive front lighting systems (AFS). In response to this, projector type vehicle headlights are often used because of requests for smaller illumination surfaces.
In contrast to this, Japanese Patent Laid-Open Publications Nos. 2004-127830 and 2005-100766 disclose vehicle headlights with bulbs facing sideways in the longitudinal direction and arranged lower than the optical axis of the projection lens. Therefore, arranging the bulb sideways makes it possible to shorten the entire length of the light fixture.
In this type of projector type vehicle headlight, a diffusion region is formed in the light distribution pattern by the region on the side of the optical axis of the reflecting surface, reflecting light from the bulb and then guiding it to the projection lens. In this vehicle headlight, the bulb is arranged lower than the optical axis, and is inserted inside the light fixture from the side. Consequently, notching is not needed in the region on the side of the optical axis of the reflecting surface. This makes it possible to form a diffusion region that has a sufficient quantity of light without reducing the quantity of light of the diffusion region in the light distribution pattern.
In the vehicle headlight disclosed in Japanese Patent Laid-Open Publications Nos. 2004-127830 and 2005-100766, however, the bulb is arranged sideways, thereby shortening the length of the entire vehicle headlight in the direction of the optical axis and resulting in a shorter configuration in the lengthwise direction overall.
When using an HID light source as a bulb however, the shortening effect due to the bulb facing sideways is approximately 50 mm.
Because of this, it is difficult to respond to demands for smaller designs for vehicle headlights as described above, which result in even smaller designs as are being asked for.
When using an HID light source with the bulb arranged sideways, the light in the direction of the center axis with the strongest light intensity is irradiated onto the diffusion region without being irradiated towards the area close to the center in the forward direction. This results in light utilization efficiency from the bulb dropping and the strongest light intensity close to the center in the light distribution pattern becoming lower.
From among the light irradiated from the bulb towards the front, the light that is not incident on the projection lens is not included in the irradiation light irradiating towards the front. Because of this, there is no contribution to the formation of the light distribution pattern, thereby resulting in the overall luminous flux becoming insufficient.
For an HID light source, the length in the optical axis direction of the light fixture can only be shortened approximately 50 mm even when the bulb is placed sideways. This makes it difficult to achieve significant shortening in the depth.
A vehicle headlight with variable light distribution is disclosed in Japanese Patent Laid-Open Publication No. 2005-166282. A dedicated reflecting surface for variable light distribution, a projection lens, and a movable reflecting surface are added to this vehicle headlight. The movable reflecting surface is opened and closed to vary the light distribution, thereby avoiding abrupt changes in the shape of the light distribution. In this headlight however, since the light source is arranged along the optical axis, shortening of the depth in the direction of the optical axis is not achieved.
In contrast, FIG. 3 shows a conventional vehicle headlight of a so-called longitudinal type. The vehicle headlight 1 is configured as a single light fixture. The vehicle headlight 1 is configured to include a bulb 2 serving as a light source, a parabolic reflecting surface 3, and a front lens 4. The parabolic reflecting surface 3 has a focus F. The light emission center of the bulb 2 is positioned close to the focus F at this time. In addition to this, the parabolic reflecting surface 3 is arranged such that the major axis extends almost horizontally towards the irradiation direction of the light. Therefore, the parabolic reflecting surface 3 reflects light from the bulb 2 towards the front. The front lens 4 is located in front of the bulb 2 and is arranged almost perpendicular to the optical axis.
The bulb 2 utilizes the bulb referred to as the C-8 light source mentioned above. The bulb 2 is arranged facing sideways from the side such that the center axis extends towards the front almost horizontally perpendicular with optical axis of the projection lens.
The intensity distribution of the C-8 light source is comparatively low at the front and rear sides (longitudinal direction along the x-axis) and is also comparatively high in the upper/lower and left/right directions (perpendicular directions in the y and z-axes).
The reflecting surface 3 is formed into a comparatively narrow longitudinal shape matching the longitudinal shape of the entire vehicle headlight 1. Because of this, the reflecting surface 3 is not well suited to obtain light distribution properties which spread out horizontally left and right.
By providing a lens cut 4a that takes into consideration the characteristics of the reflecting surface 3, the front lens 4 radiates light reflected by the reflecting surface 3 as well as direct light from the bulb 2 in the horizontal direction left and right.
The light emitted from the bulb 2 in the vehicle headlight 1 with this type of configuration is either directly incident on the projection lens 4 or is reflected by the reflecting surface 3, forming an almost parallel light and then is incident on the projection lens 4. The incident light is radiated in the horizontal direction left and right by the projection lens 4 and is then irradiated towards the front.
The reflecting surface 3 in the conventional configuration of the longitudinal type vehicle headlight 1 described above also has a longitudinal shape and a narrow width. Because of this, the quantity of the incident light emitted from the bulb 2 reflecting incident to the reflecting surface 3 is reduced and the light utilization efficiency of the bulb drops.
For example, when using a tungsten halogen lamp as the bulb 2 in the configuration described above, the greatest brightness in the light distribution pattern is approximately 260 lm which is comparatively dark as shown in FIG. 4A.
In this type of conventional vehicle headlight 1, the light reflected by the longitudinal reflecting surface 3 is radiated in the horizontal direction left and right by the front lens 4. Therefore, a lens cut 4a in the front lens 4 that radiates in the horizontal direction left and right is essential. This results in less freedom in the design of the lens.
When the front lens 4 is arranged in an almost perpendicular manner, an appropriate light distribution pattern is obtained as shown in FIG. 4A. When the design is such that the front lens 4 is arranged at a slant, the light distribution region in the region at both ends of the light distribution pattern will fall downward or rise upward as shown in FIG. 4B. As a result, this light distribution pattern is not suitable as a light distribution pattern for a vehicle headlight.
In contrast to this, the use of a so-called C-6 light source in which the longitudinal direction of the light emitting portion is positioned at a right angle to the optical axis is also considered. Even though this light source is used, the incident efficiency towards the reflecting surface 3 worsens and the light utilization efficiency drops. For this case, it is difficult to obtain a bright light distribution pattern together with a low incident reflection efficiency due to the narrow width of the reflecting surface 3.